I have a suspicion that the slowness of Gnome-terminal compared to
others has something to do with Pango-- There's been recent talk of
optimizing Pango's paths for "standard" text, in part due to Mozilla's
consideration of using it for a layout engine. I suspect if pango gets
sped up, the terminal will benefit significantly.

Pango is used very little in vte. I think at this point the major
slowdown in gnome-terminal is rendering the text. If you pick a bitmap
font its a lot faster. If someone wants to optimize this they need to
work on the Xserver level to make Xrender faster. Latest Xorg version
already has some optimizations in this area.

There are also at least those two bug reports in bugzilla with profiling
info and some patches: